invention relates to a process and an apparatus for pelleting materials capable of forming drops.
Materials capable of forming drops are generally pelleted in such a manner that the materials to be pelleted are fed into a refrigerant bath which preferably comprises a liquefied gas such as liquid nitrogen.
An apparatus for pelleting viscose liquids is shown in DE 37 11 169 C2. In this apparatus a dropping apparatus is situated above a liquid nitrogen bath in which there is a transport belt, from which dropping apparatus uniform drops exit which sink in the liquid nitrogen bath and are transported out by the conveyor belt. The completely frozen pellets are then stored cold at a product-dependent temperature.
GB 2 092 880 B shows an apparatus in which the material to be pelleted is added dropwise to a bath of a coolant liquid, the liquid drops to be frozen being washed by a horizontal coolant stream onto a take-off apparatus before they lose their buoyancy. In a separation apparatus, the pellets are separated off and the refrigerant is recirculated to the refrigerant bath.
U.S. Pat. No. 4,843,840 shows an apparatus for a process in which the liquids to be frozen are precooled both by direct contact with the refrigerant in pipes and by indirect contact by return circuits of the used refrigerant by means of contact ducts running in parallel. After separating off the refrigerant, the particles thus precooled are completely frozen solid in the cold gas stream.
In the apparatus according to DE 37 11 169 C2, depending on the product to be processed, complex cleaning operations can be involved on the transport belt which itself is driven by a complex mechanism. The cold gas formed in the use of this apparatus is utilized only to a small extent in this process.
In the apparatus of GB 2 092 880, there is the disadvantage that amounts of refrigerant need to be transported over relatively long pathways, which leads to complex types of insulation and, if this measure is dispensed with, to high evaporation losses, in particular when liquid nitrogen is used as refrigerant. Refrigerant which has already evaporated is not utilized in this process either.
In the apparatus of U.S. Pat. No. 4,843,840, although the cold gas formed from the evaporation process in the precooling is utilized for complete freezing solid, the conveyer screw used for the secondary cooling, owing to the high number of precooled particles which are fed simultaneously from a plurality of cooling pipes running in parallel, is fed with such a large amount of particles that keeping the particles separate which is necessary for the production of high-rate pellet products is not achieved. In addition, a considerable expenditure in terms of machinery is connected with the said apparatus.